Nonlinear dielectric ceramic, pulse generating capacitor, high-pressure vapor discharge lamp circuit, and high-pressure vapor discharge lamp

ABSTRACT

A nonlinear dielectric ceramic having the D-E hysteresis characteristics contains a barium titanate-based compound as a principal constituent and a nonreducing oxide glass as a secondary constituent, and thus the nonlinear dielectric ceramic has reduction resistance. A pulse generating capacitor including the nonlinear dielectric ceramic, a high-pressure vapor discharge lamp circuit including the pulse generating capacitor, and a high-pressure vapor discharge lamp including the pulse generating capacitor are also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to nonlinear dielectric ceramics for pulsegenerating capacitors which are used as starters of discharge lamps,pulse generating capacitors in which dielectric ceramics are used asdielectric materials, and high-pressure vapor discharge lamps in whichthe capacitors are used as starters. More particularly, the inventionrelates to a nonlinear dielectric ceramic which is suitable for ahigh-pressure vapor discharge lamp having a starter contained in a bulb.

2. Description of the Related Art

High-pressure vapor discharge lamps, such as a high-pressure sodiumlamp, are difficult to start using a commercially-used power-supplyvoltage and the application of a high pulse voltage is required.

High-pressure vapor discharge lamps, in which starters for generatinghigh pulse voltages are contained in discharge-lamp bulbs and thestarters are utilized in combination with ballasts for generalhigh-pressure mercury lamps, have come into wide use. Such ahigh-pressure vapor discharge lamp basically includes a luminous tubeand a capacitor using a nonlinear dielectric ceramic, the luminous tubeand the capacitor being connected in parallel, and by combining asolid-state switch (SSS) therewith, a high pulse voltage is generated.The high pulse voltage together with a power-supply voltage is appliedto the luminous tube to start the discharge lamp.

As a means for stably generating such a high pulse voltage, a pulsegenerating capacitor including a nonlinear dielectric ceramic composedof a barium titanate-based compound as a dielectric material has beenused.

The pulse generating capacitor has a D-E hysteresis curve in whichelectric displacement (D) changes steeply in relation to voltage (E), asshown in FIG. 1. If a voltage that is larger than the coercive electricfield of the capacitor is applied, the electric charge is abruptlysaturated in the vicinity of a polarization inversion voltage. A changein the electric current at this stage also causes a change in ballast,and a high pulse voltage corresponding to −L·di/dt can be generated dueto the inductance of the ballast.

The pulse generating capacitor used for a high-pressure vapor dischargelamp such as a high-pressure sodium lamp must have a steep slope of theD-E hysteresis curve, which must be stable over a wide temperaturerange. Pulse generating capacitors which meet the above requirements aredisclosed in Japanese Unexamined Patent Publication Nos. 63-221504,63-221505, 1-136323, 1-136324, etc.

The bulb of a high-pressure vapor discharge lamp, such as ahigh-pressure sodium lamp, is usually maintained at a high vacuum ofapproximately 1×10⁻⁵ torr, and is exposed in a high-temperature highvacuum of 300° C./1×10⁻⁵ torr. A barium getter for adsorbing oxygengenerated during lighting is also disposed in the bulb of the dischargelamp so that the degree of vacuum in the bulb is maintained. However, ifthe discharge lamp continues to be lit, a reducing atmosphere isproduced in the bulb due to hydrogen adsorbed by members such as aluminous tube, the metallic support for the luminous tube, the glassconstituting the bulb, and hydrogen generated by the decomposition ofadsorbed water.

Therefore, if the pulse generating capacitors disclosed in JapaneseUnexamined Patent Publication Nos. 63-221504, 63-221505, 1-136323,1-136324, etc. are used in bulbs for a long period of time, thedielectric ceramics are reduced and the insulation resistance isdecreased, resulting in a low or no pulse voltage being generated, andhence the discharge lamp is not lit.

In order to cope with the above problems, as disclosed in JapaneseUnexamined Patent Publication No. 60-52006, the pulse generatingcapacitor except for a current-carrying section is entirely coated withinorganic glass, or as disclosed in Japanese Unexamined PatentPublication No. 4-34832, a getter for adsorbing hydrogen is disposed inthe bulb. However, deterioration is not fully suppressed by the abovemeasures, and the structures of the pulse generating capacitors anddischarge lamps may become complex, resulting in an increase in cost.Additionally, if the pulse generating capacitor is entirely coated withinorganic glass as disclosed in Japanese Unexamined Patent PublicationNo. 60-52006, the D-E hysteresis characteristics of the dielectricceramic is degraded by the glass, and it may become difficult to obtaina high pulse voltage. Furthermore, production problems may be caused.For example, inconsistencies in the characteristics in the differentdielectric ceramic lots may be increased, and warpage may occur in theceramic when it is fired.

SUMMARY OF THE INVENTION

Accordingly, it is a main object of the present invention to provide anonlinear dielectric ceramic which is suitable as a dielectric materialfor obtaining inexpensive pulse generating capacitors, in which thecharacteristics are not degraded even if exposed in high-temperaturehigh vacuum during lighting and in a reducing atmosphere during use, ahigh pulse voltage can be generated over a wide temperature range, andinconsistencies in characteristics are decreased, thus enabling stablecharacteristics in terms of production.

It is another object of the present invention to provide a pulsegenerating capacitor in which a nonlinear dielectric ceramic is used asa dielectric material.

It is another object of the present invention to provide a high-pressurevapor discharge lamp circuit or a high pressure vapor discharge lampwhich uses the pulse generating capacitor as a starter.

In accordance with the present invention, a nonlinear dielectric ceramichaving the D-E hysteresis characteristics contains a bariumtitanate-based compound as a principal constituent and a nonreducingoxide glass as a secondary constituent, and thus the nonlineardielectric ceramic has reduction resistance.

The content of the nonreducing oxide glass is preferably set at about0.8 parts by weight or less relative to 100 parts by weight of thebarium titanate-based compound.

Preferably, the nonreducing oxide glass contains at least one of Si andLi.

Preferably, the nonreducing oxide glass is one of a first nonreducingoxide glass and a second nonreducing oxide glass, the first nonreducingoxide glass being represented by the formula Li₂O—(Si, Ti)O₂—MO (whereMO is at least one of Al₂O₃ and ZrO₂), and the second nonreducing oxideglass being represented by the formula SiO₂—TiO₂—XO (where XO is atleast one oxide selected from the group consisting of BaO, CaO, SrO,MgO, ZnO and MnO).

Preferably, the first nonreducing oxide glass is represented by theformula xLi₂O-y(SiwTi_(1−w))O₂-zMO (where MO is at least one of Al₂O₃and ZrO₂, x, y, and z refer to mole %, and subscript w satisfies therelationship 0.30≦w≦1.0). In the ternary composition diagram shown inFIG. 2, the ratio (x, y, z) lies within a polygon, including the sidesof the polygon, obtained by linking point A (20, 80, 0), point B (10,80, 10), point C (10, 70, 20), point D (35, 45, 20), point E (45, 45,10) and point F (45, 55, 0), (wherein w satisfies the relationship0.30≦w<1.0 if the ratio lies on the line A-F).

Preferably, the second nonreducing oxide glass is represented by theformula xSiO₂-yTiO₂-zXO (where XO is at least one oxide selected fromthe group consisting of BaO, CaO, SrO, MgO, ZnO and MnO and x, y, and zrefer to mole %). In the ternary composition diagram shown in FIG. 3,the ratio (x, y, z) lies within a polygon, including the sides of thepolygon, obtained by linking point A (85, 1, 14), point B (35, 51, 14),point C (30, 20, 50) and point D (39, 1, 60).

Preferably, the second nonreducing oxide glass contains at least one ofAl₂O₃ and ZrO₂ in an amount of about 15 parts by weight or less in total(where the content of Zro₂ is about 5 parts by weight or less) relativeto 100 parts by weight of the SiO₂—TiO₂—XO-based nonreducing oxideglass.

Preferably, the second nonreducing oxide glass contains at least one ofLi₂O and B₂O₃ in an amount of about 20 parts by weight or less in totalrelative to 100 parts by weight of the SiO₂—TiO₂—XO-based nonreducingoxide glass.

Preferably, the barium titanate-based compound is represented by theformula(Ba_(1−x−y−z)Sr_(x)Ca_(y)Mg_(z)O)_(m)·(Ti_(1−o−p)Zr_(o)Hf_(p))O₂,wherein subscripts x, y, z, m, o, and p satisfy the relationships0≦x≦0.05, 0≦y≦0.02, 0≦z≦0.005, 0.995≦m≦1.02 and 0.035≦o+p≦0.12 (where0≦o≦0.12 and 0≦p≦0.12).

Preferably, the nonlinear dielectric ceramic contains an oxide of atleast one element selected from the group consisting of La, Ce, Nd, Pr,Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Y in an amount of about 0.5 mole orless relative to 100 mole of the barium titanate-based compound.

Preferably, the nonlinear dielectric ceramic contains an oxide of atleast one element selected from the group consisting of Mn, Ni, and Coin an amount of about 0.5 mole or less relative to 100 mole of thebarium titanate-based compound.

Preferably, the nonlinear dielectric ceramic contains an oxide of atleast one element selected from the group consisting of La, Ce, Nd, Pr,Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Y and an oxide of at least oneelement selected from the group consisting of Mn, Ni, and Co in anamount of about 1.0 parts by weight or less in total relative to 100parts by weight of the barium titanate-based compound.

A pulse generating capacitor in accordance with the present invention isused in a bulb of a high-pressure vapor discharge lamp, and thecapacitor includes a dielectric material and electrodes formed on thedielectric material. The dielectric material is composed of thenonlinear dielectric ceramic.

A high-pressure vapor discharge lamp circuit in accordance with thepresent invention includes a series circuit composed of the pulsegenerating capacitor and a switch and a luminous tube, the seriescircuit being electrically connected to the luminous tube in parallel.

A high-pressure vapor discharge lamp in accordance with the presentinvention includes the pulse generating capacitor and a luminous tubewhich are electrically connected to each other in parallel and enclosedin a bulb.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of a D-E hysteresis loop of a nonlinear dielectricceramic used for a capacitor in accordance with the present invention;

FIG. 2 is a ternary composition diagram of an Li₂O—(Si, Ti)O₂—MO-basednonreducing oxide glass;

FIG. 3 is a ternary composition diagram of an SiO₂—TiO₂—XO-basednonreducing oxide glass;

FIG. 4 is a sectional view of a pulse generating capacitor in accordancewith the present invention;

FIG. 5 is a sectional view of a high-pressure vapor discharge lamp inaccordance with the present invention;

FIG. 6 is a lamp circuit diagram including the high-pressure vapordischarge lamp shown in FIG. 5;

FIG. 7 is a circuit diagram for pulse generation and measurement; and

FIG. 8 is a graph which shows the relationship between the lighting timeand pulse voltage generated.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Nonlinear dielectric ceramics, pulse generating capacitors,high-pressure vapor discharge lamp circuits, and high-pressure vapordischarge lamps in the present invention will be described withreference to the drawings.

FIG. 4 is a sectional view of a pulse generating capacitor including anonlinear dielectric ceramic in accordance with the present invention.The pulse generating capacitor A is produced by the following method.First, a binder is added to a starting ceramic powder having apredetermined composition. After drying and granulation are performed, adisk-shaped green compact is obtained by pressing or the like. The greencompact is fired and a nonlinear dielectric ceramic 1 as a dielectricelement is obtained. Next, a pair of electrodes 2 are formed on bothprincipal surfaces of the nonlinear dielectric ceramic 1. An insulatingglass 3 is formed in a ring for insulation, and lead terminals 4 areelectrically connected to the electrodes 2 with a conductive adhesive 5or the like, and thus the pulse generating capacitor A is obtained.

The nonlinear dielectric ceramic contains a barium titanate-basedcompound as a principal constituent and a nonreducing oxide glass as asecondary constituent. Thus, the reduction resistance of the ceramicitself and the steep hysteresis characteristics are obtained, and evenif exposed in a high-temperature high vacuum and in a reducingatmosphere, the insulation resistance is not decreased and a high pulsevoltage is generated. That is, although the reduction resistance is notobtained only by having the barium titanate-based compound as theprincipal constituent, the reduction resistance of the ceramic itself isobtained by including the nonreducing oxide glass.

By including the nonreducing oxide glass, inconsistencies in the grainsize of the ceramic are reduced and the breakdown voltage is improved asthe generated pulse voltage is increased. Furthermore, by including atleast an oxide of at least one element selected from the groupconsisting of Mn, Ni and Co and an oxide of at least one elementselected from the group consisting of La, Ce, Nd, Pr, Sm, Eu, Gd, Tb,Dy, Ho, Er, Yb and Y, the generated pulse voltage is further increased.

FIG. 5 is a sectional view of a high-pressure vapor discharge lamp inaccordance with the present invention, and FIG. 6 is a lamp circuitdiagram including the high-pressure vapor discharge lamp. In thehigh-pressure vapor discharge lamp B, a luminous tube 11 and a pulsegenerating capacitor A that is connected to the luminous tube 11 inparallel are enclosed in a bulb 12, and a solid-state switch 13 isconnected to the pulse generating capacitor A in series. An AC voltageis applied to the high-pressure vapor discharge lamp B through a ballast14 from an AC power source 15 so that the high-pressure vapor dischargelamp B is lit.

The present invention will be described in more detail based on theexamples. However, it is to be understood that the present invention isnot limited to such examples.

EXAMPLE 1

First, BaCO₃, SrCO₃, CaCO₃, MgCO₃, TiO₂, ZrO₂ and HfO₂ having puritiesof 99% or more were prepared as starting materials.

Next, the above materials were mixed so that barium titanate-basedcompounds represented by the formula(Ba_(1−x−y−z)Sr_(x)Ca_(y)Mg_(z)O)_(m)·(Ti_(1−o−p)Zr_(o)Hf_(p))O₂ wereobtained, in which subscripts x, y, z, m, o, and p were set as shown inTable 1. The mixed materials were subjected to wet blending with a ballmill, and grinding was performed, followed by drying. Calcining was thenperformed in air at 1, 120° C. for 2 hours. The resultant calcines wereground by a dry grinder, and raw materials having a grain size of 1 μmor less were obtained.

TABLE 1 First nonreducing Second nonreducing Sample(Ba_(1-x-y-z)Sr_(x)Ca_(y)Mg_(z)O)_(m).(Ti_(1-o-p)Zr_(o)Hf_(p))O₂ oxideglass oxide glass No. x y z m o p o + p (parts by weight) (parts byweight) *1 0.01 0.015 0.002 0.997 0.03 0.02 0.05 0 0  2 0.04 0.008 0.0031.010 0.06 0.02 0.08 1.5 0  3 0.03 0.005 0.001 1.015 0.01 0.08 0.09 01.5  4 0.08 0.01 0.004 1.000 0.02 0.05 0.07 0 0.05  5 0.04 0.05 0.0031.003 0.02 0.02 0.04 0.3 0  6 0.02 0.003 0.010 0.999 0.08 0.03 0.11 00.4  7 0.02 0.012 0.003 1.008 0.005 0.005 0.01 0.1 0  8 0.01 0.016 0.0021.012 0.11 0.07 0.18 0 0.2  9 0.03 0.004 0.004 0.990 0.06 0.02 0.08 0.60 10 0.02 0.008 0.003 1.050 0.01 0.03 0.04 0.05 0 11 0.04 0.001 0.0011.001 0.05 0.05 0.1 0.005 0 12 0.03 0.012 0.004 1 0.04 0.02 0.06 0 0.00513 0.04 0.005 0.002 1.005 0.07 0.01 0.08 0.01 0 14 0.01 0.016 0.003 1.010.06 0.03 0.09 0 0.2 15 0.02 0.01 0.002 1.003 0.04 0.03 0.07 0.8 0 160.03 0.018 0.004 1.008 0.05 0.01 0.06 0 0.8 17 0.05 0.007 0.004 0.9980.04 0.06 0.1 0 0.05 18 0 0.016 0.001 1.013 0.12 0 0.12 0.5 0 19 0.040.02 0.002 1.006 0 0.12 0.12 0 0.01 20 0.01 0 0.001 1.001 0.06 0.05 0.110.2 0 21 0.03 0.008 0.005 1.005 0.02 0.03 0.05 0 0.5 22 0.01 0.013 01.015 0.06 0.01 0.07 0 0.1 23 0.02 0.005 0.002 1.007 0.025 0.01 0.0350.1 0 24 0.04 0.012 0.003 1.012 0.07 0.05 0.12 0 0.3 25 0.04 0.01 0.0040.995 0.02 0.06 0.08 0.01 0 26 0.02 0.015 0.003 1.02 0.03 0.01 0.04 0.050 *Out of the scope of the present invention

As the first nonreducing oxide glass, a powder was obtained by weighing,mixing, and grinding the oxide, carbonate, or hydroxide of eachconstituent so as to satisfy the composition of

0.25Li₂O-0.65(0.30TiO₂·0.70SiO₂)-0.10Al₂O₃ (molar ratio).

Similarly, as the second nonreducing oxide glass, a powder was obtainedby weighing, mixing and grinding the oxide, carbonate, or hydroxide ofeach constituent so as to satisfy the composition of

0.66SiO₂−0.17TiO₂−0.15BaO−0.02MnO (molar ratio).

Next, each of the powder obtained was separately placed in a platinumcrucible and was heated to 1,500° C., followed by quenching. Bysubsequent grinding, the first and second nonreducing oxide glasspowders having average grain sizes of 1 μm or less were obtained.

The starting powders were weighed so as to achieve the compositionsshown in Table 1, to which 3% by weight of polyvinyl alcohol and purewater were added, followed by wet blending by a ball mill. After dryingand granulation, forming was performed at a pressure of 2 tons/cm² anddisk-shaped green compacts were obtained. The resultant green compactswere fired for 2 hours at the temperatures shown in Table 2, andnonlinear dielectric ceramics having a diameter of 18 mm and a thicknessof 0.6 mm were obtained.

Electrodes having a diameter of 16 mm were formed on both principalsurfaces of each of the nonlinear dielectric ceramics. The electrodeswere formed by baking a silver paste. Furthermore, for the purpose ofinsulation, crystallized glass was formed into a ring having an outerdiameter of 17 mm and an inside diameter of 14 mm, and lead terminalswere connected, and thus a pulse generating capacitor A was produced. Asthe lead terminal, a nickel wire was used, which was connected by asilver paste.

Generated pulse voltages of the capacitors obtained as described abovewere measured at temperatures of −40° C., room temperature and 50° C.,respectively, using the pulse generation and measurement circuit shownin FIG. 7. The pulse generation and measurement circuit included acircuit in which the pulse generating capacitor A produced as describedabove was placed in a temperature control unit, and a solid-state switch23 having a breakover voltage of 150 V and a 400 W mercury lamp ballast24 (input voltage: 220V, 60 Hz) were connected in series, which wasconnected to an AC power source 25 (100 V, 60 Hz). The generated pulsevoltages were measured by an oscilloscope 26 that was connected betweenterminals of the series circuit of the pulse generating capacitor A andthe solid-state switch 23.

Next, using an insulation testing set, the insulation resistance of thecapacitor was measured by applying a direct-current voltage of 100 V for2 minutes, and the volume resistivity p of the dielectric ceramic wascomputed.

In order to measure the change in characteristics over time in ahigh-temperature reducing atmosphere, the capacitor was left in a vacuumchamber under the conditions of 400° C., 1×10⁻⁵ torr, and a hydrogenconcentration of 0.5% for 1,000 hours, and then generated pulse voltagesat room temperature (20° C.) were measured using the pulse generationand measurement circuit shown in FIG. 7. The insulation resistance wasalso measured and the volume resistivity ρ was computed.

As a high-temperature load test, samples in which silver electrodeshaving a diameter of 17 mm were baked on both principal surfaces ofnonlinear dielectric ceramics having a diameter of 18 mm and a thicknessof 0.6 mm were prepared, and pulse voltages after applying adirect-current voltage of 100 V for 240 hours in an isothermal chambermaintained at 125° C. were measured using the pulse generation andmeasurement circuit shown in FIG. 7.

Furthermore, as an AC dielectric breakdown test, samples in which silverelectrodes having a diameter of 14 mm were baked on both principalsurfaces of nonlinear dielectric ceramics having a diameter of 18 mm anda thickness of 0.6 mm were prepared, and while applying an alternatingcurrent of 60 Hz under a pressure at 100 Vrms/sec., voltages in whichdielectric breakdown occurred in the samples (AC dielectric breakdownvoltages) were measured.

The results of the individual tests were shown in Table 2.

TABLE 2 Firing 400° C./1 × 10⁻⁵ Torr/ 125° C./100 V/240 hr AC dielectrictemper- Generated pulse voltage (kV) Volume 0.5% H₂/1000 hr GeneratedVolume breakdown Sample ature Room resistivity ρ Generated pulse Volumeresistivity pulse resistivity voltage No. (° C.) −40° C. temperature 50°C. (Ω · m) voltage (kV) ρ (Ω · m) voltage (kV) ρ (Ω · m) (kV/mm) *1 14701.38 1.34 1.31 4.42 × 10¹² 0.71 8.68 × 10⁷  1.31 4.37 × 10¹¹ 5.12  21300 1.47 1.45 1.37 2.87 × 10¹² 1.44  .59 × 10¹² 1.41 2.87 × 10¹² 6.86 3 1310 1.52 1.48 1.41 8.27 × 10¹¹ 1.46 8.25 × 10¹¹ 1.41 8.02 × 10¹¹6.92  4 1350 1.91 1.87 1.51 2.87 × 10¹¹ 1.87 2.84 × 10¹¹ 1.83 2.84 ×10¹¹ 6.31  5 1370 1.56 1.54 1.32 2.21 × 10¹² 0.84 4.34 ′ 108  1.51 2.21× 10¹² 6.54  6 1470 1.50 1.47 1.38 4.18 × 10¹¹ 0.79 5.92 × 10⁷  1.434.13 × 10¹¹ 6.27  7 1380 1.56 1.52 1.43 8.40 × 10¹¹ 1.51 8.30 × 10¹¹1.49 8.14 × 10¹¹ 6.38  8 1350 1.63 1.61 1.22 1.91 × 10¹² 1.62 1.88 ×10¹² 1.58 1.89 × 10¹² 6.51  9 1300 1.92 1.89 1.81 2.68 × 10¹² 0.97 2.68× 10⁸  1.80 2.65 × 10¹² 4.33 10 1470 1.52 1.48 1.39 1.81 × 10¹² 1.471.80 × 10¹² 1.45 1.79 × 10¹² 6.98 11 1390 1.91 1.87 1.83 1.08 × 10¹²1.83 1.07 × 10¹² 1.83 1.08 × 10¹² 6.02 12 1380 1.91 1.88 1.81 2.82 ×10¹² 1.81 2.83 × 10¹² 1.80 2.83 × 10¹² 6.08 13 1360 2.06 2.02 1.94 2.21× 10¹² 2.00 2.21 × 10¹² 1.98 2.20 × 10¹² 6.28 14 1380 2.09 2.05 1.963.14 × 10¹² 2.03 3.12 × 10¹² 2.01 3.15 × 10¹² 6.61 15 1320 1.97 1.941.89 2.44 × 10¹² 1.90 2.43 × 10¹² 1.88 2.44 × 10¹² 6.72 16 1350 1.971.93 1.85 3.45 × 10¹² 1.85 3.45 × 10¹² 1.83 3.43 × 10¹² 6.65 17 13902.00 1.98 1.90 6.53 × 10¹² 1.96 6.54 × 10¹² 1.94 6.51 × 10¹² 6.12 181360 1.97 1.94 1.86 6.31 × 10¹² 1.92 6.30 × 10¹² 1.90 6.31 × 10¹² 6.7819 1380 2.08 2.04 1.91 7.14 × 10¹² 2.00 7.12 × 10¹² 1.98 7.12 × 10¹²6.34 20 1390 2.03 2.01 1.93 6.42 × 10¹² 1.93 6.42 × 10¹² 1.910 6.39 ×10¹² 6.49 21 1370 1.95 1.92 1.84 3.23 × 10¹² 1.90 3.23 × 10¹² 1.88 3.23× 10¹² 6.69 22 1360 2.00 1.96 1.87 3.33 × 10¹² 1.94 3.32 × 10¹² 1.923.33 × 10¹² 6.58 23 1370 1.88 1.84 1.81 4.83 × 10¹² 1.80 4.82 × 10¹²1.78 4.79 × 10¹² 6.32 24 1330 1.99 1.97 1.84 5.39 × 10¹² 1.89 5.40 ×10¹² 1.87 5.40 × 10¹² 6.67 25 1300 1.97 1.94 1.88 2.95 × 10¹² 1.92 2.95× 10¹² 1.9 2.95 × 10¹² 6.04 26 1390 1.97 1.93 1.82 5.36 × 10¹² 1.89 5.35× 10¹² 1.87 5.34 × 10¹² 6.85 *Out of the scope of the present invention

As is obvious from Tables 1 and 2, when a pulse generating capacitorusing the nonlinear dielectric ceramic in accordance with the presentinvention, which contains a barium titanate-based compound representedby the formula(Ba_(1−x−y −z)Sr_(x)Ca_(y)Mg_(z)O)_(m)·(Ti_(1−o−p)Zr_(o)Hf_(p))O₂,wherein subscripts x, y, z, m, o, and p satisfy the relationships0≦x≦0.05, 0≦y≦0.02, 0≦z≦0.005, 0.995≦m≦1.02, 0≦o≦0.12, 0≦p≦0.12 and0.035≦o+p≦0.12, as a principal constituent and a nonreducing oxide glassas a secondary constituent, a high pulse voltage of 1.8 kV or more isgenerated in the temperature range of −40° C. to 50° C. Moreover, evenif exposed in a high-temperature reducing atmosphere, the insulationresistance is not decreased and the generated pulse voltage is notdecreased. Furthermore, the AC dielectric breakdown voltage is as highas 6 kVrms/mm or more.

The reason for preferable limitations on the compositions of thenonlinear dielectric ceramic containing a barium titanate-based compoundrepresented by the formula(Ba_(1−x−y−z)Sr_(x)Ca_(y)Mg_(z)O)_(m)·(Ti_(1−o−p)Zr_(o)Hf_(p))O₂ as aprincipal constituent and a nonreducing oxide glass as a secondaryconstituent will be described.

When the content of the nonreducing oxide glass is zero in relation tothe barium titanate-based compound, as in sample No. 1, by being exposedin a high-temperature reducing atmosphere, the dielectric ceramic isreduced, the insulation resistance is decreased and the pulse voltage issignificantly decreased, which is undesirable. As in sample Nos. 2 and3, when the content of the nonreducing oxide glass is more than 0.8parts by weight in relation to the barium titanate-based compound, thepulse voltage does not exceed 1.8 kV. With respect to the content of thenonreducing glass, as in sample Nos. 11 and 12, although even at aslight amount of 0.005 parts by weight, satisfactory results areobserved. By setting the content at 0.01 to 0.2 parts by weight, moresatisfactory results are observed.

As in sample No. 4, when the Sr content x exceeds 0.05, the pulsevoltage at 50° C. does not exceed 1.8 kV. By setting the Sr content at0.05 or less, the generated pulse voltage can be increased.

As in sample No. 5, when the Ca content y exceeds 0.02, the generatedpulse voltage is decreased. By setting the Ca content y at 0.02 or less,a decrease in the generated pulse voltage in a high-temperature reducingatmosphere can be prevented. As in sample No. 6, when the Mg content zexceeds 0.005, the generated pulse voltage does not exceed 1.8 kV. Bysetting the Mg content z at 0.005 or less, the reduction resistance isimproved, and a decrease in the generated pulse in a high-temperaturereducing atmosphere does not easily occur.

Furthermore, as in sample No. 7, when the total o+p of the Zr content oand the Hf content p is less than 0.035, the generated pulse voltage isdecreased. On the other hand, as in sample No. 8, when the total o+p ofthe Zr content o and the Hf content p exceeds 0.12, the generated pulsevoltage does not exceed 1.8 kV.

As in sample No. 9, when the molar ratio m is less than 0.995, ifexposed in a high-temperature reducing atmosphere, the dielectricceramic is reduced, the insulation resistance is decreased and thegenerated pulse voltage is significantly decreased. The AC dielectricbreakdown also does not exceed 6 kV/mm. On the other hand, as in sampleNo. 10, when the molar ratio m exceeds 1.02, the generated pulse voltageis decreased.

EXAMPLE 2

In a manner similar to that in example 1, raw materials for a bariumtitanate-based compound represented by the formula

(Ba_(0.958)Sr_(0.03)Ca_(0.01)Mg_(0.0002)O)_(1.003)·(Ti_(0.92)Zr_(0.06)Hf_(0.02))O₂

were prepared. Li₂O—(Si, Ti)O₂—MO-based (where MO is at least one ofAl₂O₃ and ZrO₂) first nonreducing oxide glass was added thereto, thefirst nonreducing oxide glass having the compositions and amounts shownin Table 3, produced at temperatures of 1,200° C. to 1,500° C., andhaving an average grain size of 1 μm or less. At the firing temperaturesshown in Table 4, and otherwise in a manner similar to that in example1, pulse generating capacitors were produced. The size and shape of thepulse generating capacitors were the same as those in example 1.

Next, in a manner similar to that in example 1, the generated pulsevoltage, the volume resistivity and the AC dielectric breakdown voltagewere obtained. The results are shown in Table 4.

TABLE 3 First nonreducing oxide glass Sample Amount added Composition(mole %, excluding w) No. (parts by weight) Li₂O (Si_(w)Ti_(1−w))O₂ wAl₂O₃ ZrO₂ 101 0.01 20 80 0.3 0 0 102 0.08 10 80 0.6 5 5 103 0.15 10 700.5 20  0 104 0.1 35 45 1 10  10  105 0.05 45 45 0.5 10  0 106 0.01 4555 0.3 0 0 107 0.12 20 70 0.6 5 5 108 0.06 20 70 0.4 10  0 109 0.18 3060 0.7 5 5 110 0.05 30 60 0.8 10  0 111 0.1 40 50 0.6 5 5 112 0.07 40 500.9 0 10  113 0.03 10 85 0.4 5 0 114 0.16  5 75 0.6 10  10  115 0.12 2055 0.5 25  0 116 0.05 45 40 0.8 0 15  117 0.03 50 45 0.7 5 0 118 0.14 2575 0.9 0 0 119 0.11 25 75 1 0 0 120 0.1 35 65 0.9 0 0 121 0.06 35 65 1 00 122 0.13 20 70 0.2 0 10 

TABLE 4 Firing 400° C./1 × 10⁻⁵ Torr/ 125° C./100 V/240 hr AC dielectrictemper- Generated pulse voltage (kV) Volume 0.5% H₂/1000 hr GeneratedVolume breakdown Sample ature Room resistivity ρ Generated pulse Volumeresistivity pulse resistivity voltage No. (° C.) −40° C. temperature 50°C. (Ω · m) voltage (kV) ρ (Ω · m) voltage (kV) ρ (Ω · m) (kV/mm) 1011380 1.98 1.95 1.90 3.28 × 10¹² 1.91 3.27 × 10¹² 1.87 2.14 × 10¹² 6.08102 1350 1.94 1.92 1.89 2.08 × 10¹² 1.88 2.08 × 10¹² 1.82 1.17 × 10¹²6.42 103 1360 2.00 1.97 1.93 3.91 × 10¹² 1.93 3.89 × 10¹² 1.89 2.65 ×10¹² 6.51 104 1370 1.95 1.93 1.90 6.28 × 10¹² 1.89 6.29 × 10¹² 1.83 4.79× 10¹² 6.41 105 1350 1.92 1.89 1.85 1.88 × 10¹² 1.85 1.87 × 10¹² 1.801.02 × 10¹² 6.25 106 1340 1.94 1.91 1.88 2.06 × 10¹² 1.87 2.06 × 10¹²1.81 1.52 × 10¹² 6.13 107 1380 1.96 1.94 1.89 6.62 × 10¹² 1.90 6.61 ×10¹² 1.84 6.14 × 10¹² 6.47 108 1370 1.95 1.93 1.89 3.51 × 10¹² 1.89 3.50× 10¹² 1.89 2.87 × 10¹² 6.31 109 1350 1.90 1.87 1.82 3.06 × 10¹² 1.833.04 × 10¹² 1.84 2.55 × 10¹² 6.59 110 1340 1.88 1.86 1.82 4.15 × 10¹²1.82 4.15 × 10¹² 1.83 3.76 × 10¹² 6.24 111 1380 1.95 1.92 1.89 5.26 ×10¹² 1.88 5.25 × 10¹² 1.90 4.71 × 10¹² 6.36 112 1340 1.95 1.93 1.89 5.66× 10¹² 1.89 5.67 × 10¹² 1.88 5.02 × 10¹² 6.34 113 1470 1.37 1.34 1.292.45 × 10¹⁰ 0.75 6.68 × 10⁷  1.31 9.67 × 10⁸  5.23 114 1470 Unable tomeasure due to insufficient sintering 115 1470 Unable to measure due toinsufficient sintering 116 1470 1.52 1.48 1.44 5.42 × 10¹⁰ 0.74 7.69 ×10⁷  1.44 1.90 × 10⁸  5.16 117 1470 1.44 1.41 1.38 5.91 × 10¹⁰ 0.72 4.06× 10⁷  1.39 4.40 × 10⁸  5.19 118 1360 1.89 1.84 1.81 5.84 × 10¹² 1.825.83 × 10¹² 1.81 5.84 × 10¹² 6.62 119 1470 Unable to measure due toinsufficient sintering 120 1350 1.91 1.87 1.83 5.39 × 10¹² 1.83 5.39 ×10¹² 1.82 5.38 × 10¹² 6.51 121 1470 1.63 1.61 1.59 2.44 × 10¹⁰ 0.76 8.66× 10⁷  1.52 6.53 × 10⁸  5.02 122 1470 Unable to measure due toinsufficient sintering

As is obvious from Tables 3 and 4 with respect to the first nonreducingoxide glass represented by the formula xLi₂O-y(SiwTi_(1−w))O₂-zMO (whereMO is at least one of Al₂O₃ and ZrO₂, x, y, and z refer to mole %, andsubscript w satisfies the relationship 0.30≦w≦1.0), when, in the ternarycomposition diagram shown in FIG. 2, the ratio (x, y, z) lies within apolygon, including the sides of the polygon, obtained by linking point A(20, 80, 0), point B (10, 80, 10), point C (10, 70, 20), point D (35,45, 20), point E (45, 45, 10) and point F (45, 55, 0), (where wsatisfies the relationship 0.30≦w≦1.0 if the ratio lies on the lineA-F), namely, in sample Nos. 101 to 112, 118 and 120, the generatedpulse voltage exceeds 1.8 kV, and even if exposed in a high-temperaturereducing atmosphere, the generated pulse voltage is not easilydecreased.

In contrast, when the Li₂O—(SiwTi_(1−w))O₂—MO-based nonreducing oxideglass is out of the compositional range described above, as in sampleNos. 113 to 117, 119, 121 and 122, either sintering becomes insufficientor the pulse voltage does not exceed 1.8 kV and the AC dielectricbreakdown voltage does not exceed 6 kV/mm.

EXAMPLE 3

In a manner similar to that in example 1, raw materials for a bariumtitanate-based compound represented by the formula

(Ba_(0.958)Sr_(0.03)Ca_(0.01)Mg_(0.002)O)_(1.003)·(Ti_(0.92)Zr_(0.06)Hf_(0.02))O₂

were prepared. SiO₂—TiO₂—XO-based (where XO is at least one oxideselected from the group consisting of BaO, CaO, SrO, MgO, ZnO and MnO)second nonreducing oxide glass was added thereto, the second nonreducingoxide glass having the compositions and amounts shown in Table 5,produced at temperatures of 1,200° C. to 1,500° C., and having anaverage grain size of 1 μm or less. At the firing temperatures shown inTable 6, and otherwise in a manner similar to that in example 1, pulsegenerating capacitors were produced. The size and shape of the pulsegenerating capacitors were the same as those in example 1.

Next, in a manner similar to that in example 1, the generated pulsevoltage, the volume resistivity and the AC dielectric breakdown voltagewere obtained. The results are shown in Table 6.

TABLE 5 Second nonreducing oxide glass Amount Major constituents (mole%) Sample added (parts XO Additive (parts by weight) No. by weight) SiO₂TiO₂ BaO CaO SrO MgO ZnO MnO Total Al₂O₃ ZrO₂ Li₂O B₂O₃ 201 0.05 85  1 1 0 0 0 4 9 14 0 0 0 0 202 0.11 35 51 0 10 0 0 0 4 14 0 0 0 0 203 0.12 3020 0 30 0 15  4 1 50 0 0 0 0 204 0.06 39  1 20  20 2 0 13  5 60 0 0 0 0205 0.08 70 10 5  5 0 0 10  0 20 0 0 0 0 206 0.15 45 10 0  0 0 0 15  30 45 0 0 0 0 207 0.1 50 20 10  10 3 7 0 0 30 0 0 0 0 208 0.07 50 30 0 16 00 0 4 20 0 0 0 0 209 0.13 35 30 25  10 0 0 0 0 35 0 0 0 0 210 0.06 40 4010   0 0 0 5 5 20 0 0 0 0 211 0.12 45 22 3 30 0 0 0 0 33 15  0 0 0 2120.05 45 22 3 30 0 0 0 0 33 10  5 0 0 213 0.15 50 30 0 16 0 0 0 4 20 0 05 0 214 0.06 35 51 0 10 0 0 0 4 14 0 5 0 5 215 0.14 70 10 5  5 0 0 10  020 0 0 20  0 216 0.1 30 20 0 30 0 15  4 1 50 0 0 0 10  217 0.03 65 25 5 5 0 0 0 0 10 0 0 0 0 218 0.14 25 40 15   0 10  0 5 5 35 0 0 0 0 2190.01 30 10 30  25 0 0 5 0 60 0 0 0 0 220 0.1 50  0 35  15 0 0 0 0 50 0 00 0 221 0.16 45 22 30   0 0 3 0 0 33 25  0 0 0 222 0.03 45 22 30   0 3 00 0 33 0 15  0 0 223 0.18 30 60 10   0 0 0 0 0 10 0 0 0 0 224 0.05 30 200 30 0 15  4 1 50 0 0 10  15  225 0.16 50 20 10  10 3 7 0 0 30 0 0 25  0

TABLE 6 Firing 400° C./1 × 10⁻⁵ Torr/ 125° C./100 V/240 hr AC dielectrictemper- Generated pulse voltage (kV) Volume 0.5% H₂/1000 hr GeneratedVolume breakdown Sample ature Room resistivity ρ Generated pulse Volumeresistivity pulse resistivity voltage No. (° C.) −40° C. temperature 50°C. (Ω · m) voltage (kV) ρ (Ω · m) voltage (kV) ρ (Ω · m) (kV/mm) 2011370 1.92 1.89 1.84 2.06 × 10¹² 1.85 2.06 × 10¹² 1.86 1.79 × 10¹² 6.24202 1360 2.03 2.01 1.97 2.43 × 10¹² 1.99 2.42 × 10¹² 1.94 2.01 × 10¹²6.51 203 1350 1.95 1.92 1.87 3.45 × 10¹² 1.87 3.45 × 10¹² 1.88 2.85 ×10¹² 6.53 204 1370 2.00 1.97 1.91 2.68 × 10¹² 1.94 2.66 × 10¹² 1.94 2.14× 10¹² 6.31 205 1350 1.95 1.93 1.88 3.79 × 10¹² 1.89 3.79 × 10¹² 1.873.34 × 10¹² 6.43 206 1360 2.12 2.09 2.01 6.18 × 10¹² 2.04 6.19 × 10¹²2.04 5.87 × 10¹² 6.64 207 1370 2.07 2.05 1.99 6.94 × 10¹² 2.01 6.93 ×10¹² 2.01 6.49 × 10¹² 6.48 208 1370 2.06 2.02 1.97 2.00 × 10¹² 1.99 2.01× 10¹² 1.99 1.74 × 10¹² 6.35 209 1340 1.90 1.87 1.82 6.06 × 10¹² 1.836.05 × 10¹² 1.85 5.81 × 10¹² 6.54 210 1380 1.88 1.86 1.81 3.55 × 10¹²1.83 3.53 × 10¹² 1.82 3.23 × 10¹² 6.32 211 1340 1.94 1.92 1.87 3.96 ×10¹² 1.88 3.96 × 10¹² 1.90 3.65 × 10¹² 6.52 212 1370 1.91 1.93 1.86 4.21× 10¹² 1.90 4.20 × 10¹² 1.88 4.01 × 10¹² 6.22 213 1360 1.94 1.90 1.841.86 × 10¹² 1.86 1.85 × 10¹² 1.84 1.66 × 10¹² 6.24 214 1350 1.91 1.891.82 7.94 × 10¹² 1.86 7.91 × 10¹² 1.83 7.88 × 10¹² 6.34 215 1380 1.951.91 1.85 5.72 × 10¹² 1.86 5.68 × 10¹² 1.84 5.55 × 10¹² 6.12 216 13701.96 1.93 1.86 6.88 × 10¹² 1.88 6.81 × 10¹² 1.85 6.61 × 10¹² 6.28 2171470 1.51 1.45 1.42 6.49 × 10¹⁰ 0.86 2.03 × 10⁷  1.42 3.89 × 10⁸  5.67218 1470 Unable to measure due to insufficient sintering 219 1470 1.551.52 1.43 2.43 × 10¹⁰ 0.81 5.67 × 10⁷  1.48 6.75 × 10⁸  5.35 220 1470Unable to measure due to insufficient sintering 221 1470 Unable tomeasure due to insufficient sintering 222 1470 1.42 1.37 1.29 3.79 ×10¹⁰ 0.79 6.02 × 10⁷  1.34 6.34 × 10⁸  5.76 223 1470 Unable to measuredue to insufficient sintering 224 1470 1.62 1.58 1.44 2.52 × 10¹² 1.562.46 × 10¹² 1.55 2.39 × 10¹² 6.22 225 1470 1.63 1.61 1.45 5.03 × 10¹²1.61 4.99 × 10¹² 1.59 4.88 × 10¹² 6.16

As is obvious from Tables 5 and 6 with respect to the second nonreducingoxide glass represented by the formula represented by the formulaxSiO₂-yTiO₂-zXO (where XO is at least one oxide selected from the groupconsisting of BaO, CaO, SrO, MgO, ZnO and MnO, and x, y, and z refer tomole %), when, in the ternary composition diagram shown in FIG. 3, theratio (x, y, z) lies within a polygon, including the sides of thepolygon, obtained by linking point A (85, 1, 14), point B (35, 51, 14),point C (30, 20, 50) and point D (39, 1, 60), namely, in sample Nos. 201to 216, the generated pulse voltage is as high as 1.8 kV or more, andeven if exposed in a high- temperature reducing atmosphere, thegenerated pulse voltage is not easily decreased.

In contrast, when the SiO₂—TiO₂—XO-based nonreducing oxide glass is outof the compositional range described above, as in sample Nos. 217 to225, the pulse voltage does not exceed 1.8 kV and the AC dielectricbreakdown voltage does not exceed 6 kV/mm.

As in sample Nos. 211 and 212, by including Al₂O₃ and/or ZrO₂ in theSiO₂—TiO₂—XO-based oxide glass, pulse generating capacitors whichgenerate pulse voltages that exceed 1.8 kV are obtained. However, as insample Nos. 221 and 222, if the content of Al₂O₃ exceeds about 15 partsby weight or the content of ZrO₂ exceeds about 5 parts by weight, thepulse voltage is significantly decreased.

As in sample Nos. 213 to 216, by including Li₂O and/or B₂O₃ in theSiO₂—TiO₂—XO-based oxide glass, pulse generating capacitors whichgenerate pulse voltages that exceed 1.8 kV are obtained. However, as insample Nos. 224 and 225, if the total content of Li₂O and B₂O₃ exceedsabout 20 parts by weight relative to 100 parts by weight of theSiO₂—TiO₂—XO-based nonreducing oxide glass, the pulse voltage does notexceed 1.8 kV.

EXAMPLE 4

In a manner similar to that in example 1, raw materials for a bariumtitanate-based compound represented by the formula

(Ba_(0.958)Sr_(0.03)Ca_(0.01)Mg_(0.002)O)_(1.003)·(Ti_(0.92)Zr_(0.06)Hf_(0.02))O₂

a first nonreducing oxide glass represented by the formula

0.25Li₂O-0.65(0.30TiO₂·0.70SiO₂)−0.10Al₂O₃ (molar ratio)−

and a second nonreducing oxide glass represented by the formula

0.66SiO₂O₂−0.17TiO₂−0.15BaO−0.02MnO (molar ratio)

were prepared.

Next, metal oxides having purities of 99% or more were prepared,including CoO, MnCO₃, NiO, La₂O₃, Nd₂O₃, CeO₂, Pr₆O₁₁, Sm₂O₃, Eu₂O₃,Gd₂O₃, Tb₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Yb₂O₃ and Y₂O₃.

The first and second nonreducing oxide glasses and the metal oxidesdescribed above were added to the raw materials for the bariumtitanate-based compound described above so as to satisfy thecompositions shown in Table 7, and at the sintering temperatures shownin Table 8, and otherwise in a manner similar to that in example 1,pulse generating capacitors were produced. The size and shape of thepulse generating capacitors were the same as those in example 1.

Next, in a manner similar to that in example 1, the generated pulsevoltage, the volume resistivity and the AC dielectric breakdown voltagewere obtained. The results are shown in Table 8.

TABLE 7 First non-reducing Second non-reducing Sample oxide glass oxideglass MnO NiO CoO Total La₂O₃ CeO₂ Nd₂O₃ Pr₆O₁₁ Sm₂O₃ Eu₂O₃ Gd₂O₃ No.(parts by weight) (parts by weight) (a) (b) (c) (a)˜(c) (d) (e) (f) (g)(h) (i) (j) 301 0.1 0 0.3 0.3 0.2 0.8 0.2 0 0 0 0.1 0 0 302 0.2 0 0.10.3 0 0.4 0 0.3 0 0 0 0 0 303 0.6 0 0 0.05 0.3 0.35 0 0 0 0.3 0 0 0 3040 0.05 0.4 0.1 0.3 0.8 0.1 0 0 0 0 0 0 305 0 0.02 0.1 0.1 0.1 0.3 0 0.40.2 0 0 0 0.2 306 0 0.08 0 0.05 0 0.05 0 0 0 0.3 0.1 0 0 307 0.01 0 0.30.1 0.1 0.5 0 0 0 0 0 0 0 308 0.2 0 0 0.2 0.05 0.25 0 0.2 0 0 0 0.1 0309 0.1 0 0.2 0.1 0.05 0.35 0 0.1 0 0.2 0 0 0 310 0 0.1 0.2 0.2 0.1 0.50 0 0 0 0 0 0.1 311 0 0.05 0 0 0 0 0 0 0.1 0 0 0.3 0 312 0 0.5 0.3 00.05 0.35 0.1 0 0 0.1 0 0 0 313 0.01 0 0.2 0.3 0 0.5 0 0 0 0 0 0 0 3140.3 0 0 0 0.3 0.3 0 0.1 0 0 0.1 0 0 315 0.8 0 0.2 0.05 0.1 0.35 0 0.1 00.2 0 0 0 316 0 0.1 0.3 0 0.2 0.5 0 0 0 0 0 0 0 317 0 0.08 0 0.1 0.2 0.30 0 0 0 0 0 0 318 0 0.06 0.4 0 0 0.4 0.1 0 0 0.1 0 0 0.1 Sample Tb₂O₃Dy₂O₃ Ho₂O₃ Er₂O₃ Yb₃O₃ Y₂O₃ Total Amount added (a)˜(p) No. (k) (l) (m)(n) (o) (p) (d)˜(p) (parts by weight) 301 0 0 0 0 0.1 0 0.4 0.84 302 00.2 0 0.2 0 0.1 0.8 0.95 303 0 0 0 0 0.1 0 0.4 1.57 304 0 0 0.1 0.2 0 00.4 0.87 305 0 0 0 0 0 0 0.8 0.8 306 0 0 0 0 0 0 0.4 1.46 307 0.2 0 0 00 0.1 0.3 0.56 308 0 0 0.2 0 0 0 0.5 0.61 309 0 0 0 0 0 0 0.3 1 310 00.1 0 0 0 0 0.2 0.46 311 0 0 0 0 0 0.1 0.5 0.68 312 0 0.1 0 0 0.1 0 0.41 313 0 0 0 0 0 0 0 0.15 314 0.1 0 0 0.1 0 0.1 0.5 0.68 315 0 0 0 0 0 00.3 1 316 0 0 0.3 0 0 0 0.3 0.63 317 0 0 0 0 0.1 0.2 0.3 0.45 318 0 0 00.1 0 0 0.4 1

TABLE 8 Firing 400° C./1 × 10⁻⁵ Torr/ 125° C./100 V/240 hr AC dielectrictemper- Generated pulse voltage (kV) Volume 0.5% H₂/1000 hr GeneratedVolume breakdown Sample ature Room resistivity ρ Generated pulse Volumeresistivity pulse resistivity voltage No. (° C.) −40° C. temperature 50°C. (Ω · m) voltage (kV) ρ (Ω · m) voltage (kV) ρ (Ω · m) (kV/mm) 3011340 1.55 1.48 1.41 2.86 × 10¹¹ 1.49 2.85 × 10¹¹ 1.11 8.08 × 10⁸  6.28302 1330 2.07 2.04 1.68 4.84 × 10¹⁰ 1.73 4.85 × 10¹⁰ 2.02 4.81 × 10¹⁰6.37 303 1390 1.68 1.62 1.54 6.05 × 10¹² 1.61 6.04 × 10¹² 1.61 6.03 ×10¹² 6.72 304 1330 1.61 1.55 1.51 6.38 × 10¹¹ 1.53 6.38 ′ 108  1.24 4.19× 10⁸  6.21 305 1320 2.09 2.05 1.63 4.06 × 10¹⁰ 1.77 4.04 × 10¹⁰ 2.024.05 × 10¹⁰ 6.08 306 1350 1.59 1.54 1.43 4.42 × 10¹² 1.54 4.41 × 10¹²1.51 4.42 × 10¹² 6.24 307 1370 2.11 2.07 2.02 6.53 × 10¹² 2.98 6.53 ×10¹² 2.07 6.51 × 10¹² 6.12 308 1350 2.08 2.06 1.97 6.83 × 10¹² 2.06 6.82× 10¹² 2.05 6.84 × 10¹² 6.45 309 1360 2.14 2.11 2.06 2.66 × 10¹² 2.122.67 × 10¹² 2.12 2.65 × 10¹² 6.31 310 1370 2.17 2.13 2.08 6.48 × 10¹²2.11 6.46 × 10¹² 2.12 6.48 × 10¹² 6.34 311 1350 2.11 2.08 2.03 3.63 ×10¹² 1.98 3.62 × 10¹² 2.1 3.62 × 10¹² 6.18 312 1370 2.08 2.06 1.96 3.52× 10¹² 2.06 3.52 × 10¹² 2.04 3.53 × 10¹² 6.68 313 1380 2.12 2.10 2.052.68 × 10¹² 2.12 2.68 × 10¹² 1.97 2.66 × 10¹² 6.11 314 1350 2.13 2.081.99 3.02 × 10¹² 2.09 3.01 × 10¹² 2.08 3.00 × 10¹² 6.56 315 1360 2.112.09 2.04 6.50 × 10¹² 2.07 6.51 × 10¹² 2.07 6.48 × 10¹² 6.84 316 13402.08 2.06 1.98 6.38 × 10¹² 2.05 6.37 × 10¹² 2.08 6.38 × 10¹² 6.29 3171370 2.15 2.12 2.07 2.67 × 10¹² 2.12 2.66 × 10¹² 2.11 2.66 × 10¹² 6.02318 1360 2.12 2.08 2.01 3.51 × 10¹² 2.09 3.50 × 10¹² 2.08 3.51 × 10¹²6.23

As is obvious from Tables 7 and 8, by including either an oxide of atleast one element selected from the group consisting of Mn, Ni and Co,or an oxide of at least one element selected from the group consistingof La, Ce, Nd, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Y, in an amount ofabout 0.5 parts by weight or less relative to 100 parts by weight of thebarium titanate-based compound, as in sample Nos. 307 to 318, thegenerated pulse voltage is as high as 1.8 kV/mm or more, and even ifexposed in a high-temperature reducing atmosphere, the generated pulsevoltage is not easily decreased, which is desirable.

In contrast, as in sample Nos. 302 and 305, if the content of the oxideof at least one element selected from the group consisting of La, Ce,Nd, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Y exceeds about 0.5 molerelative to 100 mole of the barium titanate-based compound, the pulsevoltage at high temperatures does not exceed 1.8 kV.

As in sample Nos. 301 and 304, if the content of the oxide of at leastone element selected from the group consisting of Mn, Ni and Co exceedsabout 0.5 mole relative to 100 mole of the barium titanate-basedcompound, the pulse voltage at room temperature is decreased. Changesover time due to high-temperature load are also increased.

As in sample Nos. 303 and 306, if the total content of the oxide of atleast one element selected from the group consisting of La, Ce, Nd, Pr,Sm, Eu, Gd, Th, Dy, Ho, Er, Yb and Y and the oxide of at least oneelement selected from the group consisting of Mn, Ni and Co exceedsabout 1.0 parts by weight relative to 100 parts by weight of the bariumtitanate-based compound, the pulse voltages at room temperature and hightemperatures do not exceed 1.8 kV.

EXAMPLE 5

A pulse generating capacitor A, which was within the scope of thepresent invention, according to sample No. 310 in example 4 wasprepared. A high-pressure sodium lamp as a high-pressure vapor dischargelamp in which the capacitor A was enclosed in a bulb was produced.

As a comparative example, a pulse generating capacitor B, which was outof the scope of the present invention, according to sample No. 1 inexample 1, was prepared. A high-pressure sodium lamp in which thecapacitor B was enclosed in a bulb was produced.

As another comparative example, a high-pressure sodium lamp in which thecapacitor B was enclosed in a bulb and a hydrogen-adsorbing getterhaving the ratio Zr/Al=87/13 (weight percentage) was also provided inthe bulb was produced.

With respect to the above high-pressure sodium lamps, lighting testswere conducted. A 400 W high-pressure mercury lamp ballast (inputvoltage: 220V, 60 Hz) was used for lighting and the lighting cycle wasset at 10 hour-On/1 hour-Off.

FIG. 8 shows the change in the generated pulse voltage in relation tothe lighting time. As is clear from FIG. 8, the pulse voltage does notsubstantially change in the high-pressure vapor discharge lamp inaccordance with the present invention. In contrast, the pulse voltagedecreases over time even if the hydrogen-adsorbing getter is provided inhigh-pressure sodium lamps in accordance with comparative examples.

As described above, the pulse generating capacitor using a nonlineardielectric ceramic in accordance with the present invention hasreduction resistance and has steep D-E hysteresis characteristics over awide temperature range. A high pulse voltage can also be generated overa wide temperature range, and even if exposed in a high-temperature highvacuum or in a reducing atmosphere, the characteristics are notdegraded. The pulse generating capacitor in accordance with the presentinvention does not need to be entirely coated with insulating glass andthe characteristics are not degraded by insulating glass. Furthermore,the capacitor in itself has a high AC dielectric breakdown voltage.

Therefore, by using the pulse generating capacitor in accordance withthe present invention as a ballast, a high-pressure vapor dischargelamp, such as a high-pressure sodium lamp, having excellent lightingcharacteristics can be obtained. In particular, since the pulsegenerating capacitor can be used for a high-pressure vapor dischargelamp in which a starter is built in a bulb of the discharge lamp, and itis not required to install a hydrogen-adsorbing getter in the bulb, aninexpensive high-pressure discharge lamp with a built-in starter can beobtained.

What is claimed is:
 1. A nonlinear dielectric ceramic having D-Ehysteresis characteristics and reduction resistance comprising: a bariumtitanate compound represented by the formula(Ba_(1−x−y−z)Sr_(x)Ca_(y)Mg_(z)O)_(m)·(Ti_(1−o−p)Zr_(o)Hf_(p))O₂,wherein subscripts x, y, z, m, o, and p satisfy the relationships0≦x≦0.05, 0≦y≦0.02, 0≦z≦0.005, 0.995≦m≦1.02, 0≦o≦0.12, 0≦p≦0.12 and0.035≦o+p≦0.12 as a principal constituent; and a nonreducing oxide glassas a secondary constituent; wherein the nonreducing oxide glasscomprises at least one first nonreducing oxide glass or secondnonreducing oxide glass, the first nonreducing oxide glass beingrepresented by the formula xLi₂O-y(Si_(w)Ti_(1−w))O₂-zMO where MO is atleast one of Al₂O₃ and ZrO₂, and where x, y and z refer to mole %, andsubscript w satisfies the relationship 0.30≦w≦1.0, and in a ternarycomposition diagram, the points (x, y, z) lie within a polygon,including the sides of the polygon, obtained by linking points A (20,80, 0), point B (10, 80, 10), point C (10, 70, 20), point D (35, 45,20), point E (45, 45, 10) and point F (45, 55, 0), provided that w<1.0when the point lies on the line A-F, and the second nonreducing oxideglass being represented by the formula SiO₂—TiO₂—XO where XO is at leastone oxide selected from the group consisting of BaO, CaO, SrO, MgO, ZnOand MnO.
 2. A nonlinear dielectric ceramic according to claim 1, whereinthe content of the nonreducing oxide glass is about 0.8 parts by weightor less relative to 100 parts by weight of the barium titanate compound.3. A nonlinear dielectric ceramic according to claim 2, wherein thesecond nonreducing oxide glass is represented by the formulaxSiO₂-yTiO₂-zXO where and x, y and z refer to mole %, and in a ternarycomposition diagram the point (x, y, z) lies within a polygon, includingthe sides of the polygon, obtained by linking point A (85, 1, 14), pointB (35, 51, 14), point C (30, 20, 50) and point D (39, 1, 60).
 4. Anonlinear dielectric ceramic according to claim 3, wherein the secondnonreducing oxide glass contains (a) at least one of Al₂O₃ and ZrO₂ inan amount of 15 parts by weight or less in total, and the content ofZrO₂ is about 5 parts by weight or less, relative to 100 parts by weightof the SiO₂—TiO₂—XO nonreducing oxide glass or (b) at least one of Li₂Oand B₂O₃ in an amount of about 20 parts by weight or less in totalrelative to 100 parts by weight of the SiO₂—TiO₂—XO nonreducing oxideglass or (c) both.
 5. A nonlinear dielectric ceramic according to claim4, wherein the nonlinear dielectric ceramic contains (a) an oxide of atleast one element selected from the group consisting of La, Ce, Nd, Pr,Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Y in an amount of about 0.5 mole orless relative to 100 mole of the barium titanate-based compound or (b)an oxide of at least one element selected from the group consisting ofMn, Ni, and Co in an amount of about 0.5 mole or less relative to 100mole of the barium titanate-based compound or (c) both.
 6. A pulsegenerating capacitor, adapted for use in a bulb of a high-pressure vapordischarge lamp, comprising a dielectric material and electrodes on thedielectric material, wherein the dielectric material comprises anonlinear dielectric ceramic according to claim
 5. 7. A high-pressurevapor discharge lamp circuit comprising a series circuit comprising apulse generating capacitor according to claim 6 and a switch and aluminous tube, wherein the series circuit is electrically connected tothe luminous tube in parallel.
 8. A high-pressure vapor discharge lampcomprising a pulse generating capacitor according to claim 6 and aluminous tube, wherein the capacitor and the luminous tube areelectrically connected to each other in parallel and enclosed in a bulb.9. A pulse generating capacitor, adapted for use in a bulb of ahigh-pressure vapor discharge lamp, comprising a dielectric material andelectrodes on the dielectric material, wherein the dielectric materialcomprises a nonlinear dielectric ceramic according to claim
 2. 10. Ahigh-pressure vapor discharge lamp circuit comprising a series circuitcomprising a pulse generating capacitor according to claim 9 and aswitch and a luminous tube, wherein the series circuit is electricallyconnected to the luminous tube in parallel.
 11. A high-pressure vapordischarge lamp comprising a pulse generating capacitor according toclaim 9 and a luminous tube, wherein the capacitor and the luminous tubeare electrically connected to each other in parallel and enclosed in abulb.
 12. A nonlinear dielectric ceramic according to claim 1, whereinthe nonlinear dielectric ceramic contains (a) an oxide of at least oneelement selected from the group consisting of La, Ce, Nd, Pr, Sm, Eu,Gd, Tb, Dy, Ho, Er, Yb and Y in an amount of about 0.5 mole or lessrelative to 100 mole of the barium titanate-based compound or (b) anoxide of at least one element selected from the group consisting of Mn,Ni, and Co in an amount of about 0.5 mole or less relative to 100 moleof the barium titanate-based compound or (c) both.
 13. A pulsegenerating capacitor, adapted for use in a bulb of a high-pressure vapordischarge lamp, comprising a dielectric material and electrodes on thedielectric material, wherein the dielectric material comprises anonlinear dielectric ceramic according to claim
 1. 14. A high-pressurevapor discharge lamp circuit comprising a series circuit comprising apulse generating capacitor according to claim 13 and a switch and aluminous tube, wherein the series circuit is electrically connected tothe luminous tube in parallel.
 15. A high-pressure vapor discharge lampcomprising a pulse generating capacitor according to claim 13 and aluminous tube, wherein the capacitor and the luminous tube areelectrically connected to each other in parallel and enclosed in a bulb.16. A nonlinear dielectric ceramic according to claim 1, wherein thenonreducing oxide glass comprises at least one of said first nonreducingoxide glass and at least one said second nonreducing oxide glass.
 17. Anonlinear dielectric ceramic according to claim 1, wherein the bariumtitanate-based compound is represented by said formula(Ba_(1−x−y−z)Sr_(x)Ca_(y)Mg_(z)O)_(m)·(Ti_(1−o−p)Zr_(o)Hf_(p))O₂ inwhich at least one of said subscripts x, y, z, o and p is greaterthan
 1. 18. A pulse generating capacitor, adapted for use in a bulb of ahigh-pressure vapor discharge lamp, comprising a dielectric material andelectrodes on the dielectric material, wherein the dielectric materialcomprises a nonlinear dielectric ceramic according to claim
 17. 19. Ahigh-pressure vapor discharge lamp circuit comprising a series circuitcomprising a pulse generating capacitor according to claim 18 and aswitch and a luminous tube, wherein the series circuit is electricallyconnected to the luminous tube in parallel.
 20. A high-pressure vapordischarge lamp comprising a pulse generating capacitor according toclaim 18 and a luminous tube, wherein the capacitor and the luminoustube are electrically connected to each other in parallel and enclosedin a bulb.